1. Technical Field
The present invention relates to an optical communications system suitable for carrying broadband communications traffic.
2. Related Art
Optical communications networks potentially offer very high capacities. However, in practice it has proved difficult to design appropriate switching technologies to realise the full potential of optical communications networks. Opto-electronic switching designs limit the bit-rate that can be handled by the network. Control and management of the switching function also provides further difficulties and there is a need to minimise software costs for call processing, network intelligence, network management and service management.
The present applicant's earlier international patent application WO 95/26592, to which the reader is directed for useful technical background, describes and claims an optical communications system in which a number of terminals are interconnected via passive optical networks (PONs) and by a wavelength-dependent router at the hub of the network. Each terminal includes means, such as a tuneable transmitter and receiver, that allows it to select one of a number of different wavelength channels for transmission and reception in different time slots. In this way, the switching function is distributed to the edges of the network, while the core of the network functions using partially or entirely passive routing devices. This overcomes many of the problems discussed above. However, there is a problem in that distributing the switching function to the edges of the network potentially imposes a large signalling overhead for the transmission of network control information such as bandwidth or packet requests and a resource allocation map indicating the wavelength channels and time slots allocated to each request.